Screw driver



Mar. 3, 1925. 1,528,584 w. STUMPF SCREW DRIVER Filed March 22', 1925 3114mm for Patented Mar. 3, 1925.

PATENT OFFICE.

VIALTER STUIVIPF, OF BALTIMORE, MARYLAND.

SCREW DRIVER.

Application filed March 22, 1923. Serial No. 626,948.

I '0 oZZ whom it may. concern.

Be it known that I, lVALTnR STUMPl a citizenof the United States of America, re:

siding in the county of. Baltimore, State of idaryland, have invented certain new and useful Improvements in Screw Drivers, of which the following is a specification.

The practice of driving screws by power actuated machinery particularly by means of stationary machines has beenwell understood for many years as has likewise the necessity for introducing into such machines a yielding or releasing element which will prevent injury to the screw heads or splitting or other injury to the work or material by further application of turning moment after the screw isseated. lVhile the earlier" development of screw driving machines relates mostly to stationary machines, the development of the portable power driven screw drivers began at {Illi'i()St,tl1(? same time with the flexible shaft inachin'h and even the earlier machines included releasing means in tlie forin of friction clutches and in some instances jaw clutches intended to give a more positive drive. Much of the screw driving a j paratusdescribed in the patents and in general use is in the form of attachments for drillingmachines both portable and stationary. The problems presented in the development of screw drivpr attachments to drills are peculiar to .that .art as to arrangement, driving and rigidity. and such attachments are not generallv applicable or desirable for general assembling worl: where one man drives screws continually and where there is opportunity for a power driven screw driver per se.

The present invention, as distinguished from the screw driver attachment art, .re lates to a portable electric screw driver, not intended for use as a drill, or for any purpose other than screw driving, and particularly to the combinations and arrangements of parts whereby the torque of an electric tool fIZUIIQOl casing, the spindle or screw driving shaft being guided and supported by an elongated bearing mounted in the tool casing, the latter being provided with a rigid extension to support and enclose the spindle and bearing which extension preferably carries at its lower end means for supporting and limiting the downward motion of the clutch and clutch shaft, which slides relatively to and releases automatically from the spindle.

In the accompanying drawings I have illustrated the essentials of a screw driving machine constructed in accordance with my invention.

In the drawing: 7

Figure 1, is a vertical section showing a portable electric screw driver embodying my invention in the preferred form, the section being taken on the axis of the screw driver shaft, and of the motor, showing a fraginentof the motor and the end portion of the shaft in elevation. Figure 2, is a detailed view of the clutch taken at right angles to Figure 1.

Referring to the drawings by numerals, the structure shown includes a tool casing or frame 1, in which is mounted a suitable inotor 2. preferably high speed and of the universal type, and suitable gearing 3, also mounted inside the casing for reducing the speed of said motor and transmitting it to the spindle 4, and a releasing device 5. The spindle comprises a hollow shaft 6, or driving member 6. which shaft is rigidly secured to the gear 7. of said reducing train of gears, 3. referred to hereinafter as the driving gear. The driving gear 7, has a central opening. 8. with a key slot 9. and the shaft 6,

is provided at its upper end with a projectthe end of the same and enters thrust bearing rings, 16 and 21, positioning these rings.

The end thrust of the screw driving shaft is taken up by this thrust bearing 19, comprising said rings and balls 20, rolling between the rings 16 and 21, the latter resting on the stud 10, and ring 23 and the former on the frameas aforesaid, the balls belng held in position by the-usual ballcasing 22.

The reducing train of gears, 3, previously referred to, consists of a pinion, 25, integral with the shaft, 26 of the motor 2, the pinion and shaft being preferably supported in a suitable bearing, 27, shown in the form of a metal sleeve mounted in and on the frame or easing, 1, of the tool. bearing is supported by a transverse partition or plate 29, securedbetween the two sections 30, and 31, of the casing 1. The

pinion 25, drives a larger toothed gear 33, on a stud 34, mounted in suitable bearings, 35, in the casing, which also carries a toothed pinion 37, rotating with the toothed gear 33, and of relatively small diameter. This pinion 37:, in turn, meshes with the large toothed gear, 7, secured to the spindle, or

- more particularly to the shaft 6 which is treated as .a part of the spindle, the term spindle being used in a more general way. It is of particular importance that all the bearings referred-to in the preceding paragraph are rigidly supported in the frame,

- and are elongated giving full support to the rotating parts. In this way all tendency of parts to get out of alignment "cramping or injuring the gears or the teeth is avoided;

The bearing sleeve 38, previously referred to inthe statement of invention page 2, line 3, et sequi. as supporting and guiding the ceive the screw driver screw driver shaft or spindle i and particularly the driv ng member 6, thereof, is rigidly sup orted in the frame and is of comparative y great length, fully and suf 'ficiently guiding and supporting the tool,

and eliminating anytendency to yield or chatter when the'tool is in operation.

Referring particularly to the com posite spindle or screw driver shaft, 4, the parts of which have relative motion at intervals lncident to the beginning andending of each screw drlvmg operation, the portion of'this member designated as hollow shaft 6, is pro vided at its lower end with jaw clutch member 42 which preferably have inclined jaw clutch engaging surfaces, 40. 1

The hollow 41, within the shaft, 6, is in the form of a cylindrical chamber concentric with said shaft.- In the upper end of this chamber is seated a helical spring, 43, which preferably fits the chamber transversely, and beneath the spring fitting the As shown this.

rezasea spending flat engaging face on the chuck shaft, the latter has been milled transversely tom the outside forming a transverse slot 90-of rectangular cross section extending substantially "half way through the shaft. This provides a flat surface 51, to engage the flat surface 49, of the screwdriver bit The lower end of the driven or chuck shaft 44, is enlarged as to circumference, forming a projecting peripheral shoulder 51.0, and this shoulder as shown is provided with diametrically opposite key slots, 50, extending downward from the surface 510.

To provide sufiiciently hard engaging aw clutch surfaces, the chuck shaft 44, is further encircled by-a hard collar,'52, which is 1 preferably of gear steel. This collar fits the shaft and in assembling it is passed over the top.end of the shaft and is pushed down until it engages: the shoulder, 510; The

,lower surface of the collar beingprovided with downwardly projecting lugs; or keys 53, to enter and engage the key slots, 50, in the; shoulder, 510.

"Collar 52,.is provided with upwardly disposed clutch teeth, 54 see Fig. 2, having inclined engaging surfaces 55, to engage the inclined surfaces, 40 on the hollow shaft, 6. Below the toothed portion, 56, the collar is reduced in diameter, forming a downwardly disposed peripheralshou'lder 5?.and

a depending portion 58, of smaller diarneter. The collar 52 fits'closely about the chuck shaft and the mounting of the collar-.on the shaft is intended to be practically permanent unless the teeth 54 should be destroyed and it should become necessary to provide a new collar when the parts may be separated by heating or by means of a press. i

The parts, particularlythe spindle and hearing described as extending downward from the driving gear 7, are housed and supdepending I ported and guided within the extension 39, of the'casing. This casing is provided at its lower end with a sheet metal cap, 59, of short cylindrical form and rounded as to its lower corners (SOytl-ie metal being turned in at the edges, 61, leavinga central opening 62, which receives and engages the reduced portion 58. of the collar freely. or in a sliding, fit. The upper edgeof the cap,'59, receives'and encloses the lower end of' the extension. 39,

the latter being reduced and shouldered at 63, to' receive it, and the cap being fastened to the extension in any suitable manner as by means of screws, 65. The shoulder 57 g on the collar 52 rests on the inside ofthe 'cap and the cap serves as a support-for the. driver chuck shaft, the said support being opposed .tothe spring 43 i the chuck shaft andbit when the tool is not in operation. The manner in which and supporting the screw driver bit shank enters the chuck shalt has been described, as has the manner of engaging it therein in nonrotative relation to the shaft 44. To support the screw driver bit the enlarged end of the chuck shaft is grooved circumferentially .at 66, to receive a spring ring 67 and the bottom of said groove is bored radially at (it? to rcccive a ball 69, the bore extending into the central chamber .46. The screw driver 'bit is correspondingly grooved at 70 so that when the bit is thrust, into place the ball engages the groove 70; being pressedby the spring 67. Rotation'of the ring is prevented by tab 71 on one end thereof, the ring being preferably split, which tab, ontersv a small hole, 72, leading from the groove 66 inwardly.

In operation the shaft H, is normallyadvanccd being thrust doi'vnwardby the action oi the spring 43, this causes the jaw members 40 and 54 to be normally disengaged, permitting the driven shaft 44 and the screw driver bit 47, to rotate freely relatively to the hollow driving member 6 or to remain stationary as the latter rotates. As soon, however, as pressure is applied to the screw driver bit suliicient to overcome the resist ance of the spring 43, the shaft recedes. i. e. moves upward 1nto the tubular shaft 4. per mitting the members 54 and 40 to become engaged, whenthe spindle or screw driver shaft opcrates,as an integral whole, rotating in response to the torque of the motor.

but at a comparatively reduced speed. until sutlicicnt resistance is encountered to overcome the spring. 4-3. by the action or" the inclined surfaces 55. sli-dingby one another, which again releases the chuck shaft. This operation permits the screw driver bit to be engaged with the work. the motor bcing previously in rotation. Pressure on the tool when the motor is rotating causes rotation of the composite screw driver shaft or spindlc by engagement of the jaw clutch members. such rotation being continued until unusual resistance such as the setting of the screw causes the said members to become disengaged. The motor may then be stopped or if desired it may be continued in operation until a second screw is engaged and driven. and so on. the operation being repeated, indefinitely.

The screw driver guide or centering device with which the bit is equippedconsists of a sleeve 1T0. enclosing the lower end of the bit. This sleeve is straight and open at its lowerv end at 171 and of a slightly larger diameter than the bit. The upper end is provided with an internal downwardly disposed shoulder 1752 .providing a central opening 73 otreduccd diameter and which fits the bit. At a suitable point 75 intermediate of its length the bit is grooved circumferentially and a spring ring 7 6 .is seated in the groove. This ring .76 forms a collar on \\l1l(l1,lll1( shoulder T2 is seated, the lower end (it the sleeve T0 extending down from the shouldcrto a point. just above the end ot the blade '77, thus the sleeve encloses the lower end of the bit and is spaced outar'dly therefrom providing for the admission of a helical spring 78 which encircles the bit, resting at its upper end against the ring 761. The lower end 01 the bit TT is encircled by a sliding guide member 79. which has an upper reduced portion 80 which enters the sleeve liO engaging the spring 78 and a circular upwardly disposed shoulder 81 which engages thelower end of the sleeve 170. the reduced portion 80 of the guide member is preferably torcedinto the sleeve 170 to given sulliciently permanent; connection, and the lower surface of the guide member 75) is hollowed out from the bottom in an inverted trustoconical form at 82 pro- .viding tor the admission and engagement of the screw heads. The conical formation provides for a variation in the diameterof the screw heads and the inverted hollow conical guide slides up and down on the screw driver bit co-opcrating with the blade.

,come. \Vhen the screw is seated the guide member including both the sleeves T0 and the cup portion 79. yields upwardly against the tendency of the spring 78. actuated by the pressure ot themember 79 against the material into which the screw is being driven which permits the screw to be driven in flush without resistance on the part of the guide. v ii I have thus described specifically and in detail a portable screw driving machine enr bodying the features oi my invention in the preferred form. in order that the ruuure and operation of the invention may he :luhy understood by those skilled in the art however the specific terms herein are used descriptively rather than in a limiting sense. the scope of the invention being defined 1n the claims.

\Vhat- I claim and desire to secure tcrs Patent is:

1. A portable power driven screw driver having a casing or frame. a motor secured to the frame. a screw driver: shaft, a train of re ducing gears one gear at one end of the tram being securedto the motor shaft, 2. gear at the other end of thetrain being secured to the screw driving shaft, a portion of the casing enclosing the screw driving shaft and extending downwardly from the main portion of the casing, an elongated bearing for by Letthe screw driver shaft in said portion of the casing, the screw driver shaft consisting of a driving member in the form of a ho low shaft secured to said reducing gear, a chuck shaft inside said driving member mounted to;-sli de" andfrotate relatively thereto, a spring tending to thrust saidvchuok shaft v downwardly, the chuck shaft having a sock:

et toreceive a screw driver bit, inclined jaw clutch engaging members on the lower surface of the'tubula1"drive shaft, inclined jaw clutch engaging members-on an opposeds'urface of the chuck'member and a support for the latter.

2. In a portable electric screwdriver a- ,casing,a motor and ascrew driver spindle mounted in saidcasing, a reducing train of gearmg connecting the motor to the screw driver spindle, bearings for the motor shaft,

the gears and the spindle mounted in said casing, the spindle being rigidly secured to the end gear of the train, a thrust bearing; for said gear and spindle, a-

spindle including a hollow shaft which is the member secured to said gear, a 'chuck shaft in said hollowshaft, a spring tending to thrust said chuck shaft from said hnll'ow shaft, inclined jaw clutch surfaces at the lowerend of said hollow shaft, opposed inclined jaw clutch surfaces on the chuck shaft and means for supporting the chuck shaft in opposition to the spring.

3.111 a portable electric screw drivera.

motor having a shaft, a casing a screw driver spindle, a portion of the casing enclosing the spindle forming an extension of the casing, a bearing for the spindle in said extension, the spindle including a hollow shaft, a sliding 'chuck, shaft in said hollow shaft, a spring tending to thrust the chuck shaft outwardly from said hollow shaft, inclined I aw clutch surfaces on the lower end of the hollow shaft, inclined jaw clutch surfaces opposed thereto onthe chuck shaft;

i. In a portable electric screw driver a motor, a motor shaft, a casingln which said shaft 18 mounted, a screwdriver spindle, a train of reducing gears connecting the shaft to the spindle, an extended portion of the casing enclosing-the spindle, a bearing for the spindle-in said extension, the spindle including a hollow shaft, a sliding chuck shaft in said hollow shaft, a spring tending to thrustthe I chuck shaft outwardly from said hollow, in-

clined clutch surfaces on the lower end of p the hollow shaft, inclined clutchsurfaces opposed. thereto'on the chuck shaft, said chuck shaft. being hollow, a transverse slot intersecting the end of said hollow, and a hit having a flat turface to engage the bottom of said slot. 4 y

5. In a portable electric screw driver a motor having a shaft, a casing in which said shaftis gnounted, a screw driver spindle, a train of reducing gears connecting the shaft to the spindle, a portion of the casing enclosing the spindle, a bearing for the spindle in said portion of the casing, the spindle including a hollow shaft a sliding chuck shaft in said hollow shaft, a spring tending to. thrust the chuck shaft outwardly from said llOlluW, inclined clutch surfaces opposed thereto on the chuck shaft, said chuck shaft being hollow, a transverse rectangular slot intersecting the end of said hollow, and bit having a half round surface adapted to be thrust therein, the half round portion havin a flat surface to engage the bottom of sai slot, a cap on the end of'said extension of the frame the cap having an opening to clear the chuck shaft and a shoulder on the chuck shaft engaging the inner surface oftthe cap from above to limit the motion of the chuck shaft.

6,111 a, portable electric screw driver a casing, a motor therein having a shaft, a screw driving spindle a portion of the easmg surrounding the spindle substantially throughout its length, the spindle including a hollow shaft :1 chuck shaft sliding in said hollow shaft a spring tending to expel the chuck shaft therefrom, the chuck shaft being hollowed to receive a screw driver bit, downwardly disposed inclined jaw clutch sur-- Maryland, I 

